Yesterday, Google announced App Engline Java 7 runtime as one of its 'experimental' features that is on its way towards wider availability. Here's a slice of the announcement; you can find useful code examples by heading over to the original post.

The App Engine Java 7 runtime allows
App Engine developers to keep pace with innovations in the Java
language and runtime. It is important that you begin testing your
applications with the new Java 7 runtime before the complete rollout in a
few months.
Some of the language features you now have access to include . . .